The functions of a nacelle for a turbofan engine for an aircraft are generally twofold. First, the nacelle directs air flow to the air intake of the engine while protecting the air flow from disturbances such as gusts, and the like. Second, the exterior surface profile of the nacelle minimizes the aerodynamic drag caused by the engine and its related components.
One design of a nacelle for a turbofan aircraft engine is described in U.S. Pat. No. 6,340,135 assigned to Rohr, Inc., and is shown in FIGS. 1A and 1B. As shown in FIGS. 1A and 1B, a turbofan engine assembly 10 includes a nacelle structure 22 and a fan case 16. In FIGS. 1A and 1B, one side of the nacelle structure 22 is removed for ease of illustration. The fan case 16 surrounds the fan blades 18 of an engine 12. As shown in FIG. 1B, the nacelle structure 22 includes a forward nacelle portion 24 and a rearward nacelle portion 25. As also shown in FIG. 1B, the forward nacelle portion 24 includes an outer skin 32, a noselip portion 28, an inner skin 30, and a plurality of bulkheads 34, 36 disposed between the outer skin 32 and the inner skin 30. The forward nacelle portion 24 is movably mounted to an aircraft's pylon structure 26 by a beam 52. The beam 52 permits the forward nacelle portion 24 to translate between a retracted operational position shown in FIG. 1A, and an extended service position shown in FIG. 1B. When the forward nacelle portion 24 is in the extended service position shown in FIG. 1B, an opening 40 between the aft edge of the forward nacelle portion 24 and the forward edge of the rearward nacelle portion 25 provides service access to various engine accessories, such as an engine's gearbox, electrical generators, and the like. When the forward nacelle portion 24 is in the operational position shown in FIG. 1A, the forward edge of the fan case 16 is releasably engaged with the aft edge of the inner barrel 30 to provide a substantially continuous inner surface.
The nacelle structure 22 described in U.S. Pat. No. 6,340,135 can be improved. In particular, there is a need for a nacelle structure having an interface between the inlet inner barrel and the fan case that is resistant to substantial damage from a blade out event, and can thus help to provide fly home capability following such an event. As is known in the art, a “blade out event” arises when a blade is accidentally released from a turbine's rotor, such as when a first-stage fan blade is accidentally released in a high-bypass gas turbine engine. U.S. Federal Aviation Administration (FAA) regulations require that certain structures be designed to sufficiently withstand such an event so that safe operation of an associated aircraft can be maintained. In addition, there is a need for a nacelle structure for a turbofan aircraft engine that is even lower in weight, and thus contributes to further increases in aircraft efficiency.